Determining a function of a capacitor of a passive filter circuit

Abstract

A method for determining a function of a capacitor of a passive filter circuit, which partially reduces line-conducted interference of an electrical device electrically coupled to a power supply system via the passive filter circuit. The passive filter circuit comprises the capacitor having a predefined capacitance value and a choke having a predefined inductance value. An electric capacitor voltage on the capacitor is detected. A connection voltage of the electrical device is detected. Spectral components are determined for the capacitor voltage and the connection voltage. The function of the capacitor is determined by analysing the spectral components in consideration of the inductance value of the choke by a statistical processing operation.

What is claimed is: 
     
       1. A method for determining a function of a capacitor of a passive filter circuit which reduces line-conducted interferences of an electrical device coupled electrically to a power supply system via the passive filter circuit, said passive filter circuit comprises the capacitor having a predefined capacitance value and a choke having a predefined inductance value, said method comprising:
 detecting an electrical capacitor voltage on the capacitor; 
 detecting a connection voltage of the electrical device; 
 detecting spectral components of the electrical capacitor voltage and the connection voltage; 
 evaluating the spectral components of the electrical capacitor voltage and the connection voltage taking into consideration the inductance value of the choke via a statistical processing operation; 
 determining a frequency-dependent damping of the passive filter circuit; 
 computing an estimated value for a capacitance value of the capacitor; and 
 determining the function of the capacitor from the estimated value. 
 
     
     
       2. The method of  claim 1 , wherein the capacitor is coupled at one of its connections to an electrical reference potential and is coupled at another one of its connections to an electrical phase potential. 
     
     
       3. The method of  claim 1 , further comprising detecting discretized and evaluating digitally the connection voltage and/or the electrical capacitor voltage. 
     
     
       4. The method of  claim 1 , wherein the evaluating comprises a determination of a capacitance value of the capacitor. 
     
     
       5. The method of  claim 4 , wherein the evaluating comprises a comparison of the determined capacitance value with a capacitance comparison value. 
     
     
       6. The method of  claim 1 , wherein only a part of the spectral components above a limit frequency determined by the passive filter circuit is taken into consideration for the evaluating. 
     
     
       7. The method of  claim 1 , wherein a switching state of a switching element connected in series with the capacitor is determined via the evaluating. 
     
     
       8. The method of  claim 1 , wherein the electrical device comprises an inverter. 
     
     
       9. The method of  claim 1 , wherein the passive filter circuit comprises an LCL circuit structure. 
     
     
       10. The method of  claim 1 , wherein the evaluating comprises anti-aliasing filtering. 
     
     
       11. A determination device for determining a function of a capacitor of a passive filter circuit which reduces line-conducted interferences of an electrical device coupled electrically to a power supply system via the passive filter circuit, said passive filter circuit comprises the capacitor having a predefined capacitance value and a choke having a predefined inductance value, said determination device configured to:
 detect an electrical capacitor voltage on the capacitor; 
 detect a connection voltage of the electrical device; 
 detect spectral components of the electrical capacitor voltage and the connection voltage; 
 evaluate the spectral components of the electrical capacitor voltage and the connection voltage taking into consideration the inductance value of the choke via a statistical processing operation; 
 determine a frequency-dependent damping of the passive filter circuit; 
 compute an estimated value for a capacitance value of the capacitor; and 
 determine the function of the capacitor from the estimated value. 
 
     
     
       12. An electrical device comprising:
 a connection for electrical coupling to a power supply system; 
 a passive filter circuit connected to the connection and electrically coupling the electrical device to the power supply system, said passive filter circuit configured to reduce line-conducted interferences and comprises the capacitor having a predefined capacitance value and a choke having a predefined inductance value; and 
 a determination device for determining a function of the capacitor of the passive filter circuit, said determination device configured to:
 detect an electrical capacitor voltage on the capacitor; 
 detect a connection voltage of the electrical device; 
 detect spectral components of the electrical capacitor voltage and the connection voltage; 
 evaluate the spectral components of the electrical capacitor voltage and the connection voltage taking into consideration the inductance value of the choke via a statistical processing operation; 
 determine a frequency-dependent damping of the passive filter circuit; 
 compute an estimated value for a capacitance value of the capacitor; and 
 determine the function of the capacitor from the estimated value.